You Do Need power plug adapter while traveling from Cocos (Keeling) Islands to Yemen.

Here is Why You Need An Adapter

The outlet and plug type used in Yemen are A, D and G and in Cocos (Keeling) Islands is I. This is how they look like.

Cocos (Keeling) Islands

In Cocos (Keeling) Islands, outlets of type I are in use.

Type I

Yemen

In Yemen, outlets of type A, D and G are in use.

Type A

Type D

Type G